This invention relates to a compact arrangement of elements in photographic apparatus, and in particular concerns a compact camera of the self-developing type.
In a preferred embodiment, the invention provides such a camera that has a folded optical image path and in which a surface that both reflects and transmits the image rays is free of interference from other camera elements in an optimum geometry where that surface is closely spaced above and extends laterally beyond the image surface of film exposure.
Cameras of the self-developing type are known in which an exposed film unit is processed within the camera to produce a visible image of the object focused at the image surface. The camera feeds the exposed film unit through the nip between a pair of spread rollers. The rollers spread a photoprocessing composition packaged with the film unit across the photosensitive layers to initiate formation of the visible image. Depending on the type of film, the treated film unit is maintained under light-tight conditions for a period of time sufficient for the visible image to form, or the film unit can be advanced into the ambient light substantially immediately after spreading of the processing composition. Self-developing cameras of this type are disclosed for example in U.S. Pat. Nos. 2,873,658; 3,396,647; and 3,537,370; and U.S. Pat. No. 3,415,644 discloses a film unit of the latter type, i.e. which can be transferred into ambient light directly after spreading of the processing composition.
The "picture" produced in a self-developing camera is, at least in most instances, the final photograph and hence should be sufficiently large for direct viewing. This is in contrast to a camera which records an image that is enlarged -- by enlargement on a print or by projection -- prior to viewing. To produce a satisfactorily large image at the image surface, i.e. the film plane or other surface in the camera where the film is exposed, the camera requires a relatively long optical path between the taking lens and the image surface. It is for this reason that many self-developing cameras, as well as other cameras which produce large images, are relatively bulky. This is especially true for such cameras which have rigid bodies, and accordingly many have collapsible bodies, typically incorporating folding bellows. It is also known to reduce the overall size of these cameras by folding the optical system by using mirrors or other reflectors.
The compactness of a self-developing camera having a folded optical system can be enhanced by having one reflective, "path-folding" surface overlie the image surface. As U.S. Pat. No. 3,818,498 of Zehnpfennig discloses, this can be achieved with a mechanical collimator that is reflective to rays impinging on it at certain angles, but transmissive for rays incident on it at another selected angle. The commonly-assigned patent application of Bruce K. Johnson entitled "Compact Prism Camera", Ser. No. 720,004 and filed on even date herewith, discloses an improvement in which an optical prism is used in lieu of the collimator. The prism faces provide the reflective and transmissive surfaces for folding the optical path of the camera. Regardless of what means are used, to attain maximum compactness, the reflective/transmissive surface is located close to the image surface, preferably with only a narrow clearance space between them.
Further, as the above-noted Johnson application discloses, a preferred geometry of the folded optical path calls for the dual-acting surface to extend laterally beyond the camera image surface. However, this extension of the prism, or of whatever other means provides the film-overlying surface of both reflection and transmission, beyond the image surface interferes with the conventional placement of the spread rollers. They generally are placed right next to the image surface, so that an exposed film unit advances to them with only short travel. This conventional roller placement is considered to minimize the likelihood that an exposed but unprocessed film unit will be subjected to unwanted exposure.
Thus, the attainment of an optimally-folded optical path for a highly compact self-developing camera is complicated by other factors, including the location of the spread rollers. Another factor is that the film units are preferably maintained flat in the camera, i.e. during storage, exposure, advance, and processing.
Accordingly, it is an object of this invention to provide a self-developing camera having an improved compact folded optical image path. It is also an object that the camera provide such an optical path within a rigid but compact camera body. A further object is that the camera employ a prism in the optical path and overlying the image surface.
Another object of the invention is to provide a compact arrangement for a camera of the self-developing type employing a prism for folding the optical image path and having minimal restraint on the shape and placement of the prism. It is a particular object to provide such a camera which allows space for the prism to have a geometrical configuration which can be essentially optimized with regard to folding the optical path and restricting spurious rays. Another object is that the camera arrangement facilitates locating the prism relative to the film surface for overall compactness.
It is also an object of the invention to provide a camera having the foregoing features and in which each film unit is flat while in the camera. The attainment of this object not only enhances the film exposure and processing, it also facilitates advancing the film through the camera with minimal drag and likelihood of jamming.
Other objects of the invention will in part be obvious and will in part appear hereinafter.